History of Life

• How old is the Earth?

  scientists estimate between 4,5 billion years old
• when did life on earth begin?

  3.8 billion years ago with unicellular organisms similar to bacteria
• what is a geological timescale


  a series of events in the earths history in order of how and when they occured. Sedimentary rock is used to establish this timescale
• why do we need geological timescales?

  to help date the age of life on earth and to see how/when organisms lived
• define fossil

  Fossils are remain, imprints or traces of living organisms preserved in rocks (or ice, resin, amber)
• define Palaeontology


  the study of fossils
• define a Palaeontologist


  scientist who studies fossils
• What is the fossil record

  a list of all fossils that have been found worldwide.
• why is the fossil record important?

  it provides a valuable record foe the history of life
• 5 uses of fossils

  -to determine the age of the earth

  -to determine when life first developed

  -tell us about life in the past

  -fossils show if there are similarities to present day organisms

  -fossils show how life forms started out as simple (unicellular) organisms and how they developed into more complex (multicellular) organisms.
• what is a missing link

  there are many gaps or "missing links" in the history of life. It seems as if some organisms appeared without any link to ancestors. it is any fossilized remains of a life form that has traits common to both an ancestral group and its derived descendant group
• another word for "missing links"

  transitional fossil
• an example of a missing link

  Archaeopteryx
• what was the Archaeopteryx

  links birds to dinosaurs, a birdlike creature that lived 150 mya, it had characteristics of both dinosaurs and birds
• 3 dinosaur features of Archaeopteryx

  1 teeth

  2 long bony reptile like tail

  3 claws
• 3 bird features of Archaeopteryx

  1 feathers

  2 wings

  3 wishbone
• ideal conditions for fossilization

  -quickly covered by sediment

  -minerals (found in water) available to fill cavities and harden

  -pressure to compact the sediment around a fossil and form rock

  -little oxygen for less decomposition

  -hard parts which decay slower
• why is fossilization rare?

  usually animal corpses are eaten by other animals or decomposed by bacteria before fossilization can occur. even hard parts like bones and shells are eventually destroyed through erosion and corrosion.
• how many types of fossils are there

  6
• type : petrified


  body substances replaced by minerals and 'turned to stone'
• type : impressions

  materials are pressed between layers of sand and clay, leaving an impression of their shape
• type : mold

  body breaks down and leaves a cavity behind
• type : cast

  made from the mold of the organism when minerals fill the cavity and harden
• type : trace

  mark made by living organism e.g. footprint
• type : preserved fossils in resin, ice or peat

  the absence of oxygen allows for good fossilization and preservation
• purpose of fossil dating

  establish the date of fossils and used to gain accurate data of when those organisms were around
• which is the more accurate type of fossil dating?

  Radiometric
• define half life

  the time it takes a radioactive substance to reduce by half
• explain relative dating

  combination of fossil studies and the study of various layers of rock where they are found, method includes studying positions an characteristics or horizontal layers of sedimentary rock
• explain radiometric dating

  looks at the amount of radioactive material in rock, method tests to see how much radioactive substance a fossil has changed from one form to another. the ratio of what is left of carbon-14 to the total amount of carbon-12, nitrogen-14 tells scientists how long ago an organism died
• explain difference of carbon 12 and carbon 14

  organisms contain both 'normal' carbon (carbon-12) as well as radioactive carbon (carbon-14)
• which carbon is radioactive?

  carbon-14
• what happens to carbon in organisms when it dies?

  the radioactive carbon-14 slowly decays and turns it nitrogen-14
• when was the Cambrian explosion?

  during the Palaeozoic era in the Cambrian period
• what happened in the Cambrian explosion

  all early life forms originated, especially animal groups, fossils from all present day animal phyla (except chordates) are present in rock formations from the era.
• more complex organisms were established with...

  a degree of adaptability which allowed them to survive the changes in the environment
• was there gradual flooding during the Cambrian period

  yes
• define mass extinction

  a mass extinction is when 50% or more of the Earths entire species vanish in a geological instant of a million years
• when was the biggest mass extinction?


  250 mya (Permian) - 90% of earths species wiped out - climate change, ice age, volcanic eruptions
• when was the second biggest mass extinction


  435 mya - climate change, possible ice age with a drop in sea level